The present invention relates to a fuel pump for fuel supply in an internal combustion engine and, more particularly, to a fuel pump as a high pressure pump of a fuel injector for a direct injection engine of a vehicle, directly injecting fuel into a combustion chamber from a fuel injection valve mounted on the combustion chamber of the vehicle engine, a direct injection engine employing the fuel pump and a surface treatment method for the fuel pump.
In recent years, in internal combustion engines, particularly, in gasoline engines for vehicles, it is desired to adopt cylinder fuel direct injection apparatus to improve fuel consumption characteristics, reduce emission of harmful exhaust gas, improve operation responsiveness such as accelerative characteristics, etc.
For the cylinder fuel direct injection apparatus, since gasoline is necessary to be directly injected into the cylinder of internal combustion engine even during compression stroke, a high pressure fuel pump which is able to supply gasoline at a high pressure of 3 MPa or more is required.
As a type of the high pressure fuel pump, there is a swash plate type axial plunger pump of type in which rotation of a swash plate driven by a shaft is converted into a swing motion by a swing plate, fluid is taken in, pressurized and delivered at a high pressure by a plunger reciprocating by the swing motion of the swing plate, in a housing.
This type of high pressure fuel pump is disclosed in JP A 9-236080, which fuel pump has a shaft transmitting driving force from outside, a swash plate rotated by the shaft, a swing plate converting the rotation of the swash plate into swing motion, a plurality of pistons reciprocating by the swing motion of the swing plate, a partition bellows for dividing a crank chamber accommodating the above-mentioned swash plate, a swing plate and pistons into a fuel chamber and a mechanism chamber, and in which a bearing portion transmitting driving force between the shaft and the swash plate and a bearing portion transmitting driving force between the swash plate and the swing plate are arranged in the mechanism chamber to lubricate the bearing portions with oil, and the above-mentioned plurality of pistons are arranged in the fuel chamber, whereby the pistons take in and deliver fuel.
In this high pressure fuel pump, when it is used for gasoline supply, oil of high viscosity excellent in lubrication can not be used in the mechanism chamber raising the pressure of gasoline, because there is a fear that the oil of high viscosity mixes with fuel, which affects combustion. Therefore, the crank chamber is divided into the fuel chamber and the mechanism chamber by the partition bellows.
That is, in the mechanism chamber, high viscosity oil excellent in lubrication is sealed as lubrication oil to improve wear resistance, whereby measures against wear, etc. between sliding surfaces of respective parts of the mechanism are taken.
On the other hand, in the fuel chamber of a mechanism portion generating high pressure with this construction, fuel is taken in and delivered by movement of the plurality of pistons reciprocating by swing motion of the swing plate, whereby the fuel is made high in pressure. Therefore, only gasoline of fuel exists as fluid in the fuel chamber. Therefore, the gasoline acts as lubrication oil on sliding portions of respective mechanism portions.
Further, as another type of high pressure fuel pump, a radial plunger high pressure fuel pump is disclosed in JP 10-318091. The fuel pump disclosed therein has a shaft transmitting driving force of an engine, a driving cam converting rotation of the shaft into swing motion, a plunger reciprocating through a lifter by the rotation of the driving cam and a cylinder bore taking in and delivering fuel in combination with the plunger.
In those fuel pumps, pump portions (pressurizing portions) inside the fuel chamber come necessarily to sliding under high surface pressure in fuel (gasoline), therefore, the portions are considered as main portions worn by wear because they are sliding in contact with each other.
In the mechanism portion raising pressure of fuel (gasoline) in the pump portions inside the fuel chamber, when gasoline is used as lubrication oil, it is considered that sliding portions are easily worn in the sliding mechanism portion because the viscosity of gasoline is extremely lower than usual lubrication oil.
Further, in some cases, gasoline having methyl alcohol and/or ethyl alcohol added thereto, or detracted gasoline, or the like is used as fuel. When such gasoline is used, in some cases, surroundings are apt to oxidation and wear takes place, with the gasoline mixed with water, acid components, etc. In such case, contacting portions of sliding mechanisms are to be placed in a circumstance more severe for wear and tear and it is considered that a quantity of wear and tear becomes large.
When the contact portions of slide mechanisms wear and a quantity of wear and tear increases, the efficiency of intake and delivery is likely to be reduced and the reliability is considered to be detracted.
Therefore, for each part of the slide mechanisms, durability, particularly, wear resistance and corrosion resistance in fuel with less lubrication property or in fuel mixed with acid components are required.
Further, JP A 8-35075 discloses an ion nitride layer and formation of, thereon, a surface-hardened layer composed of nitride, carbide and carbonitride of at least one kind of Ti, Zr, Hf, V, Nb, Ta and Cr by a PVD method, however, it does not disclose any specific use and any specific problem in the specific use.
Further, JP A 55-117068 discloses formation of a surface hardened layer of carburizing, nitriding, etc. on an inner surface of a fuel injection hole, and a harder coating layer than the surface hardened layer on the surface hardened layer by a CVD method (chemical vapor deposition method). JP A 55-117068 discloses, as a subject, wear and corrosion due to contact between a fluid and a solid, however, it does not touch a specific subject in the case where it is used for a fuel pump.
An object of the present invention is to provide a fuel pump, of which slide mechanism parts in a fuel chamber are excellent in wear resistance and corrosion resistance in fuel of detracted lubricative property or in fuel mixed with acid components, and a direct injection engine using the fuel pump.
The present invention resides in a fuel pump, transferring fuel to a fuel injection valve and characterized in that a film having corrosion resistance and wear resistance is formed a surface of at least one of parts contacting with each other and sliding.
The present invention resides in a fuel pump which pressurizes fuel and supplies it to a fuel injection valve of a vehicle engine.
The present invention resides in a fuel pump which pressurizes fuel and supplies it to a fuel injection valve of a vehicle engine, and which is characterized in that a surface-hardened layer comprising one of a nitride layer, a carburized and quenched layer and a carbonitrided layer, and a metal compound layer formed on the surface-hardened layer and having a higher corrosion resistance to the fuel than the surface-hardened layer is formed on at least one of sliding surfaces contacting with each other and sliding through the fuel, or the above-mentioned surface-hardened layer is formed on at least one of slide surfaces contacting with each other and sliding through lubrication oil.
The present invention resides in a fuel pump which comprises, inside a housing, a shaft transmitting rotation from outside, a swash plate converting rotation of the shaft into a swinging motion and a plunger reciprocated in a cylinder by the swinging motion of the swash plate through a slipper, and pressurizes fuel and supplies the fuel to a fuel injection valve of a vehicle engine, and which is characterized in that a surface-hardened layer comprising one of a nitride layer, a carburized and quenched layer and a carbonitrided layer, and a metal compound layer formed on the surface-hardened layer and having a higher corrosion resistance to the fuel than the surface-hardened layer is formed on at least one of sliding surfaces of the plunger and cylinder, contacting with each other and sliding, or the above-mentioned surface-hardened layer is on sliding surfaces of the swing plate and slipper, contacting with each other and sliding.
The present invention resides in a fuel pump which comprises, inside a housing, a swash plate rotating through a shaft transmitting rotation from outside, a swing plate swinging by rotation of the swash plate and a plunger reciprocating in a cylinder through a slipper by rotation of the swing plate, and pressurizes fuel and supplies the fuel to a fuel injection valve of a vehicle engine, and which is characterized in that a surface-hardened layer comprising one of a nitride layer, a carburized and quenched layer and a carbonitrided layer, and a metal compound layer formed on the surface-hardened layer and having a higher corrosion resistance to the fuel than the surface-hardened layer is formed on at least one of sliding surfaces of the plunger and cylinder, contacting with each other and sliding, or further the above-mentioned surface-hardened layer is formed on slide surfaces of the swing plate and slipper, contacting with each other and sliding.
The present invention resides in a fuel pump which comprises a shaft rotating by driving of an engine, a cam rotating by rotation of the shaft and a plunger reciprocating in a cylinder by rotation of the cam, and pressurizes fuel and supplies the fuel to a fuel injection valve of a vehicle engine, and which is characterized in that a surface-hardened layer comprising one of a nitride layer, a carburized and quenched layer and a carbonitrided layer, and a metal compound layer formed on the surface-hardened layer and having a higher corrosion resistance to the fuel than the surface-hardened layer is formed on at least one of sliding surfaces of the plunger and cylinder, contacting with each other and sliding.
The present invention resides in a direct injection engine which comprises fuel injection means for directly injecting fuel into a combustion chamber and a fuel pump supplying the fuel to said fuel injection means, and which is characterized in that said fuel pump is any one of the fuel pumps as described above.
For the surface-hardened layer according to the present invention, it is preferable to perform, after surface treatment, a treatment of heating at a higher temperature than the surface treatment to cause weak compounds to disappear. The diffusion surface treatment is performed for a nitride layer, a carbonitrided layer, a soft nitride layer, a salt bath soft nitride layer, a carburized and quenched layer or a layer made of two or more of those layers. Particularly, the diffusion treatment is performed for a nitride layer because it is treated at a low temperature of about 500xc2x0 C., whereby a weak compound layer is formed.
A hard film of corrosion resistance and wear resistance according to the present invention is preferable to be a film formed by ion-plating a metal compound selected from carbide, nitride and caronitride.
Tool steels, stainless steels, alloy steels and bearing steels can be used for slide portions contacting with each other and sliding, in the present invention.
In the present invention, a diffusion surface treatment layer and a hard layer of corrosion resistance and wear resistance are preferable to be formed by continuously treating them in one treatment bath.
Fe3N (white compound) is preferable not to be formed in a nitride layer of a diffusion surface treatment layer according to the present invention.
A nitride layer as a hardened layer in the present invention is preferable to be formed by introducing hydrogen, nitrogen or hydrogen and ammonia in a vacuum furnace and generating plasma to activate the gas.
The hard film of corrosion resistance and wear resistance according to the present invention is preferable to be formed by a physical gas phase vapor deposition method (PVD method). When a CVD method is used, a treatment temperature becomes high of 700-1100xc2x0 C., and there is a problem that when a coating layer is formed on a treatment layer such as a nitride layer, carbonitride layer, etc., the treatment layer is heated to be softened or disappear.
For a material for swash plate in the present invention, a surface treatment material of alloy steel for machine structure use or cast iron, and a surface treatment material of the cast iron.
Slipper members according to the present invention are preferable to be made of aluminum alloy, copper alloy, alloy tool steel, stainless steel, or its surface treatment material.
A cylinder according to the present invention is preferable to be made of alloy tool steel or ferrite stainless steel.
In the case where slide portions slide in gasoline of less lubricative property or in fuel in which water and alcohol are present and acid components are mixed in a mechanism part and a pump part for pressurizing fuel and delivering it, material of each slide part, its surface treatment and its combination are optimized.
The diffusion surface treatment layer has an effect that load resistance to a high surface pressure is improved and separation resistance of a hard film also is improved by raising the hardness of a base material and forming a hard film of corrosion resistance and wear resistance. In the diffusion surface treatment layer, there are a nitride layer, a carbonitrided layer, a soft nitride layer and a salt bath nitride layer as nitride for diffusing mainly nitrogen, precipitating fine nitride to raise the hardness in a temperature region in which the property of base material is not damaged. Further, a carburizing and hardening method of diffusing carbon in a high temperature region and quenching thereby to raise the hardness is applied.
Nitrides becomes higher in hardness than a base material by forming nitride by nitride-forming elements, have a property of being difficult to be adhered, and reactivity to friction and wear of the base material is improved. Further, the nitride layer is a treatment layer continued from the base material, so that it has a property that it is difficult to be separated under high surface pressure. The cementation layer can be formed as a deep treatment layer and it has an excellent load resistance when a high surface pressure is applied thereon. Corrosion resistance and wear resistance are improved by properties of the corrosion resistant and wear resistant hard film and the surface diffusion treatment layer.
With the construction, friction resistance is small, and it does not almost occur that a material on one side does not stick or adhere to a material on another side. Therefore, initial wear, steady wear and sticking or the like are prevented. Thereby a fuel pump which is excellent in reliability can be provided.